pic: In_CIM_erator

[AdamHeard]

Originally Posted by Hawiian Cadder

i made a hub out of delrin which press fit onto the rs 775 axle, on the other side it pressed onto the rs550 axle, they were both the same delrin drum which was tested.

I got a test for ya, a good ol drag race.

Lock the shafts of the two motors together, and run them opposite directions. Whichever doesn't die is the winner!

[Hawiian Cadder]

i was planning on making my delrin hub into a pulley tomorrow and see which motor will lift a little weight the fastest, we are not using either of the kit motors either so i may try a drag race, that will likely fry one or both of the motors though.

[kevin.li.rit]

Originally Posted by Hawiian Cadder

i was planning on making my delrin hub into a pulley tomorrow and see which motor will lift a little weight the fastest, we are not using either of the kit motors either so i may try a drag race, that will likely fry one or both of the motors though.

You should do a series of weights until you reach stall that way you can find peak power. You should also use a power supply to control the voltage if possible.

[Tom Line]

We engineered a component on our robot using the R775. We knew the weight, and using the calculated power of the R775 we figured it would take: 0.8 seconds to traverse the distance we needed. It performed exactly as it was engineered to, and the R775 provided the exact amount of power that it was supposed to.

I have absolutely no reason to doubt the manufacturer's specifications on these motors. They appear to be correct.

[Ether]

Just discovered this thread. From the vantage point of a month later, I suppose it is possible that Hawiian Cadder was using a defective RS775. Do you still have that motor? Do you have another RS775 you could compare it to with your "thumb test"?

A few additional remarks. Peak output power occurs at half free speed, not at stall (post #42), and not at the intersection of the torque and speed curves (unless the graph is scaled to make it so) (post #17). Kv (rpm/sec) is the velocity constant, not the motor constant. Motor constant is Km which is (stall torque)/sqrt(input watts at stall) (post #27).

[Creator Mat]

Another thing just take a look at the motors. I know this is a tad unscientific but doesn't a bigger motor generally = more power? Plus ask yourself if a manufacturer made a smaller lighter motor that was more powerful than a bigger heavier motor why would they make the bigger motor in the first place? So why is it not so off base to conclude that the RS 775 18v is more powerful than the RS 550 motor? Especially when the manufacturer's specs back up this idea.

[EricH]

Bigger motors only have more power if they aren't case shorted half the time or more.

Guess which motor has a tendency to have a case short?

[Chris is me]

Originally Posted by EricH

Bigger motors only have more power if they aren't case shorted half the time or more.

Guess which motor has a tendency to have a case short?

How does that add to the discussion about the 775's peak power?

The 550s have other reliability issues, just more obvious and less damning (i.e. trying to stall them will quickly result in smoke, while the 775s can take more abuse. when the case isn't shorted.)

[Tristan Lall]

Just to resurrect the discussion about whether the 18 V RS-775 motor from BaneBots (M7-RS775-18) is a Mabuchi product, see here and here for what a Mabuchi sold by a reseller looks like. You can clearly see the differences in case style from the Mabuchi spec sheet, and if you look closely at the first link, you can also pick up the (painted-on) Mabuchi "M" logo on the side of the case, with what appears to be a part number underneath the reseller's label.

So I stand by my contention that the Banebots RS-775 from 2011 is not a Mabuchi motor.

[Andy A.]

95 used the banebots published spec sheet to design a shoulder joint. It is operating as intended, which I would not expect to be the case if the actual motor performance and the specified performance differed by such a wide margin. Given the frictional loses we're undoubtly encountering it's a little surprising that it's performing as well as it is, truth be told. We were conservative and planned on using two of these motors ganged together, but are finding out it operates just fine on one. We'll likely use the second anyways but I wouldn't be surprised to find out the motor is operating a bit above the projected rating.

In fact, not only is it operating spot on at the design speed, it is holding level a pretty substantial arm for ~10 seconds (stalled at about 15 amps maybe) with no apparent heat issues. I'm petrified of holding any longer then that right now, but I suspect it could do it. That places it well above the FP motor in my book on the size/weight/power/reliability value matrix.

Whatever the actual performance is it's way closer to the banebots published spec then it is to 70 watts.